Fix the test runner class and the default whitelist to run.
Also add a short description about the usage.
Test: ./frameworks/base/services/tests/runtest.py with a Pixel.
Change-Id: I1a6eda83ab7b03ea11346e66ba758aa990df13c7
Developers can run this script from within a shell where they have
source'd build/envsetup.sh and lunched a target. It builds, installs,
and runs whitelisted test packages.
Bug: None
Test: This script is useful for iterating rapidly on unittests.
Change-Id: I44c32a0f75da1be2c69a8b1a67c0080a68def738